Although glioblastomas are the most malignant and common brain tumors, effective treatment strategies remain a challenge. Since current treatments are ineffective, further therapeutic approaches for this deadly disease are needed. This proposal aims to develop a dual approach to control the growth of glioblastoma by promoting differentiation and enhancing apoptosis. This can be achieved by down regulation of telomerase activity and activation of proteolysis. Preliminary results indicate that interferon-gamma (IFN-gamma) and taxol (TXL) induce modest amounts of apoptosis or programmed cell death (PCD) in human (T98G and U87MG) and rat (C6) glioblastoma cell lines. The differentiating agents, all-trans-retinoic acid (ATRA) and 13-cis-retinoic acid (13-CRA), induce differentiation and also down regulate telomerase activity in glioblastoma cells. Retinoid-treated glioblastoma cells become more sensitive to IFN-gamma or TXL for apoptosis. We hypothesize that (1) IFN-gamma or TXL activates cysteine proteases (e.g., calpain and caspase-3) by modulating levels and functions of Bcl-2 family members, (2) ATRA and 13-CRA induce differentiation and down regulate telomerase activity and Bcl-2 level and increase cell sensitivity to IFN-gamma or TXL for apoptosis, and (3) treatment of glioblastoma in animal models with a retinoid and IFN-(. or a retinoid and TXL will down regulate telomerase and enhance apoptosis. The central hypothesis of this proposal is that down regulation of telomerase activity and activation of proteolysis may effectively control glioblastoma growth. The main objective is to strategically use two treatment systems: ATRA or 13-CRA followed by IFN-gamma or TXL. To achieve this objective, the following will be examined: Specific Aim 1: Proteolysis by calpain and caspase-3 in apoptosis of glioblastoma cells exposed to IFN-gamma or TXL. Specific Aim 2: The ability of ATRA or 13-CRA to down regulate telomerase activity and Bcl-2 levels enhancing apoptosis in glioblastoma subsequently treated with IFN-gamma or TXL. Specific Aim 3: The efficacy of the combination of a retinoid and IFN-gamma or a retinoid and TXL for proteolytic control of glioblastoma in animal models. A novel technique of "combined TUNEL and double-immunofluorescent labeling" to simultaneously detect apoptosis and specific proteolysis in glioblastoma will be used. Success of our therapeutic strategy in in vitro and animal models may form a basis for treatment of glioblastoma in humans.